T' P' Yunck

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GRACE Occultation Update
T. P. Yunck COSMIC Science Workshop Boulder,
Colorado 21 August 2002
SAC-C
CHAMP
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The CHAMP Spacecraft
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Gravity Recovery and Climate Experiment GRACE
Primary Mission Objective Produce a new model
of the Earth's gravity field with unprecedent
accuracy every 12 to 25 days for five years

• System Characterics
• 480 km circular polar orbit (89)
• 200 km separation, 50 km
• 24 and 32 GHz crosslink range, with 1 micron
  accuracy
• Occultation antennas fore and aft
• BlackJack receiver performs crosslink range
  measurement, zenith POD tracking, occultation
  data collection, star tracker processing

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GRACE GPS Antennas
Occultation
Zenith POD
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• GRACE Status
• GRACE was launched without occultation software
  installed in the receivers
• A new software upload, including occultation
  software, is planned for the last week of
  September
• GRACE is still in the commissioning phase,
  performing calibrations and tuning its modes of
  operation
• A good deal of preliminary gravity data has been
  acquired and some early gravity field solutions
  have been generated
• A review will be held in late September to
  evaluate readiness for transition from
  commissioning phase to validation phase
• Validation phase is followed by Observation
  phase operationally, these phases are
  essentially the same

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• GRACE Status (cont.)
• The Project policy for activating occultations is
  still under review
• There are, however, some guiding principles
• The gravity commissioning phase must be completed
• No actions supporting occultations will be taken
  that could compromise the prime gravity mission
• A good set of clean gravity data should be
  acquired first
• The decision will be made jointly by the PI
  (Byron Tapley) and the Co-PI (Christoph Reigber)